1. Field of Invention
This invention relates to pistons of internal combustion engines, and more particularly to enhancement of the piston rings employed in such pistons.
2. Description of the Prior Art
Those skilled in the art will appreciate that the pistons of internal combustion engines in today""s modern vehicles are generally provided with three sets of piston rings for preventing, between the pistons and cylinder bores, leakage of gas to the crankcase, or of oil to the piston head.
As a practical matter, it is well known that the piston rings of modern engines, although substantially improved over engines of prior vintage, are in some ways still lacking. For example, the upper compression ring is designed for one hundred percent sealing of the gases of combustion to prevent entry into the engine crankcase. Generally the lower compression ring provides only about forty percent of the noted gas sealing function, and approximately sixty percent of an oil scrapping function. The latter prevents oil from traveling up to the top of the piston head to create the classic smoking tailpipe or xe2x80x9cblue smokexe2x80x9d syndrome. Finally, most modern pistons includes a bottom oil control ring that includes at least one rail used for aggressive scrapping of oil to force same back into the crankcase. Normally sharing the bottom piston ring groove with the at least one rail is an expander ring formed of an undulating, sinusoidal-shaped spring steel for the purpose of loading the rail appropriately, so that the rail may be effective in its scrapping function as the piston reciprocates within its cylinder bore. Hence the combination of the rail and the expander is referred to as an oil control ring.
It will thus be appreciated that various piston rings have unique design functions for addressing either of the noted prevention of leakage of gas to the crankcase, or of oil to the piston head. Generally, as the rings wear during their continuous scrapping against the cylinder walls and associated rocking within piston ring grooves, issues of blow-by of gases into the crankcase, and oil leakage into combustion chamber areas, become significant. Most rings incorporate a tangential tension in their initial structure which can generate approximately eight pounds of force (as measured by a spring band) against the cylinder walls. Unfortunately, this force does not vary, and tends to apply same pressure on both upward and the downward strokes of the piston.
Particularly with respect to the scrapper function of the bottom oil control ring, a variable oil ring compression control against the cylinder walls would be quite desirable.
The present invention provides a mechanism designed to maximize radial pressure of a piston oil control ring against the cylinder wall of a cylinder bore on the downward or power stroke of the piston. Conversely, the same mechanism minimizes the pressure on the upward stroke. For this purpose, a cam is positioned between the gap of the expander ring of the bottom control ring in the piston. The cam oscillates in response to the cyclic movement of the piston connecting rod. A shaft is rigidly affixed to the cam, and is secured to a pivot plate located within the body of the piston. The pivot plate oscillates in a rocking motion in response to a paddle slapping motion induced by the oscillatory/rotary movement of the connecting rod. The cam is positioned to reciprocally expand and contract the expander ring during the power stroke cycle. As a result, the radial pressure of the ring increases and decreases against the cylinder wall as the piston reciprocates within the cylinder. Minimizing and maximizing the normally constant radial ring pressure during the piston upstroke and downstroke, respectively, will minimize oil consumption and increase fuel economy.